Site Surveys and Preplanning - ECG...2018/04/03 · 7/27/2012 2 2012 Jim Dunlop Solar Site Surveys and Preplanning: 3 - 4 Site Surveys The objectives of a site survey include: Determine

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2012 Jim Dunlop Solar

Chapter 3

Site Surveys and Preplanning

Customer Development ● Site Assessment ●Locating PV Arrays ● Shading Analysis ● Project

Planning and Preparation

2012 Jim Dunlop Solar Site Surveys and Preplanning: 3 - 2

Overview

Objectives of a site survey.

Identifying locations for installing PV arrays and other equipment.

Assessing the type and condition of roofing systems or other structural support.

Using solar shading calculators to evaluate shading on potential PV array locations.

Evaluating electrical services and suitability for PV system interconnection.

Documenting the site layout and conditions.

Planning installation and project logistics.

Conducting a hazard assessment and safety training.


Preliminary Assessment

An initial assessment for a PV installation involves gathering information to determine the feasibility and project requirements.

Customer development: Discuss needs and expectations Complete sales, contracting and financing

Site conditions: Solar resource and environmental factors Verify electric energy consumption and costs Use satellite imagery and mapping tools

Installation preplanning: Array location and structural support Hazard assessment Design and plan review Electrical, fire, safety and building codes Equipment and manpower needs

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Site Surveys

The objectives of a site survey include:

Determine a suitable, unshaded area for installing the PV array.

Assess the type and condition of roof or other mounting surface for the array, and determine the appropriate structural attachments.

Evaluate existing electrical services and identify utility interconnection options.

Determine appropriate locations for inverters, switchgear and other equipment.

Document layout and dimensions of site, and gather any other information required for permitting and system installation planning.

Identify safety hazards, logistical and materials handling issues associated with conducting the system installation.


Site Survey Checklist

A site survey checklist is used to document site conditions relative to a PV installation, including:

Locations for installing PV arrays and other equipment

Condition of roofing and structural support

Shading issues

Environmental factors

Size of electrical services

Codes and local requirements


Site Survey Equipment

Safety Equipment Appropriate PPE including hardhats, safety glasses, safety shoes, gloves and fall

protection systems.

Tools Basic hand tools, ladders, flashlights, mirrors and magnifying glasses for

inspections.

Measuring Devices Tape measures, compasses, levels, protractors and solar shading calculators.

Electrical Meters: Voltmeters, ammeters, watt and watt-hour meters, and power analyzers.

Documentation and Record Keeping: Graph paper, calculator, audio recorders, cameras and electronic notebooks.

System Documentation: System design information or project plans as available.

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Site Survey Equipment


System Documentation

Organizing system documentation is a critical part of site surveys and preplanning, and is required for building permits, utility interconnection and some incentive programs.

Key components of a system documentation package should include: System design and equipment specifications

Site layout drawings and equipment locations

Owner/operator manuals for the system and major components

Electrical and mechanical drawings

Installation, operating and maintenance procedures

Site survey and shading analysis (required by some rebate programs)


Seaward SolarSolarCert Elements Software

Compile and store complete PV system documentation package per IEC 62446.

Create test reports, import documents and produce installation diagrams.

Export test reports and inspection certificates in PDF format.

See: www.seawardsolar.com

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Hazard Assessment

A hazard assessment is conducted during a site survey to identify all safety hazards employees may be exposed to during construction.

Primary hazards during a PV installation are electrical and fall hazards.

The employer shall eliminate the hazards where possible and train employees in the recognition and avoidance of unsafe conditions, including the proper use of PPE.


Safety Training

Safety training is provided to workers prior to beginning construction, and should cover the following areas:

Recognition and avoidance of job site hazards

Controls and work practices used to reduce or eliminate the hazards

Use and care of personal protective equipment

Proper use and storage of tools and equipment

Locations of medical and first-aid supplies

Locations and use of fire extinguishers and other safety equipment

Emergency procedures

Designated safety monitors and their responsibilities


Local Requirements

PV system installations must comply with all applicable building codes.

Interactive PV systems require interconnection approval from the local utility company.

Incentive programs may also place additional requirements on eligible PV systems.

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Environmental Conditions

The site environmental conditions have important consequences on the design and installation of PV systems.

Minimum and maximum site temperatures dictate operating limits for equipment, PV array voltage and string sizing.

The solar radiation resource determines the system energy production.

Maximum winds speeds affect the design of array mounting systems.

Other local environmental conditions may also need to be considered, such as in seismic or heavy snowfall regions.


Electrical Services

The electrical service and distribution equipment in a facility dictate the methods used and the size of the PV system that can be interconnected to the grid.

Considerations for electrical services include:

Size of distribution transformer Location of service entrance Service rating and maximum fault currents Size, ratings, location and condition of

distribution panels Condition of grounding electrode and

grounding systems.


Equipment Locations

Establish appropriate locations for system equipment based on design and code requirements, including:

Locations for installing PV arrays, inverters, batteries and other major components.

Shortest routing for conduit and wiring systems.

Consider accessibility for installation, maintenance and safety.

The NEC requires sufficient access and working space about electrical equipment (see Art. 110).

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Locating PV Arrays

A key objective of site surveys is to verify or determine a suitable location for installing PV arrays.

Factors to consider include: Available surface area and orientation

Accessibility and working spaces

Fire safety codes and wind loads

Shading obstructions

Structural attachments and support

Proximity to other equipment

Aesthetics


Array Surface Area

PV module characteristics and array layout dictate the overall surface area required for a given generation capacity.

Fire safety codes, wind loads and accessibility must be considered when evaluating suitable array locations and layouts.

National Park Service/Jim Dunlop Jim Dunlop


Array Area Calculations

Power densities for PV arrays can vary between 6 and 15 watts per square foot (W/sf), depending on module efficiency and array layout.

For a 175-watt PV module with an area of 14.4 sf, the module power density is:

175 W / 14.4 sf = 12.2 W/sf

For a 4 kW PV array, the total module surface area is:

4000 W / 12.2 W/sf = 328 sf

Approximately the area of 10 sheets of 4x8 plywood

Due to required space for access, additional area is usually required for the overall PV array installation and other equipment.

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Array Area Requirements

520 ft

250 ft

270 ft

100 ft

Space between rows for roof equipment, access and to prevent row-row shading

Total roof area approx. 100,000 sq. ft.

Approx. 50,000 sq. ft (50%) for PV array

Power density: 1 kW / 100 sq. ft.

70 kW x 3

Total Array Capacity: 500 kW

60 kW x 5

N

Electrical Training Institute, Los Angeles, CA

Google

Commercial Rooftop: 500 kW PV Array


Ground-Mounted Arrays

Site surveys for ground-mounted PV arrays should consider:

Zoning and land use issues

Terrain, elevations and grading requirements

Soil type and array ground-cover

Water table, flood zones and drainage

Array foundation requirements

Security requirements, fencing and service vehicle access


Roofing Evaluation

Roofing systems are a major consideration in the design and installation of roof-mounted PV arrays. Key items to evaluate during a site survey include:

Building type and roof design

Roof dimensions and orientation

Roof surface, condition and structural support

Roof access and fall protection methods required

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Roofing designs are classified by the shape of the roof surface and how they transmit loads to structural support members.

The type of roof design affects the usable area for installing PV arrays, due to fire safety codes, wind load distributions, and surface orientation.

Roof Designs

Hip Roof

Cross Gable RoofCross Hip Roof

Gable Roof

Monoslope Roof

Flat Roof


Roof Dimensions

Roof dimensions that affect the design, installation and performance of PV arrays include:

Roof pitch (slope)

Roof direction

Roof length, width and area

Roof pitch and slope:

2/12 = 9.5° 6/12 = 26.6°

3/12 = 14° 8/12 = 33.6°

4/12 = 18.4° 12/12 = 45°


Roofing Material

The type of roof surface affects the choice of PV mounting system attachments and weathersealing methods. Inspect roof condition during a site survey - older roofs may require

replacement prior to PV installations.

Roofing Material Life (yrs) Features

Asphalt Shingle 15-20 Low cost

Concrete Tile 30-50 Require additional structural support, not used in freeze/thaw climates

Standing Seam Metal 50+ Use zinc and aluminum coatings, require sealants on low slope roofs

Membrane & Built-Up 30+ Common for commercial flat roofs

Wood Shakes <30 Typically cedar, lightweight, combustible

Slates 100+ Very high cost

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Roof Structure

Most roof structures are capable of supporting rigidly attached PV arrays. Roofing structure details to investigate during site surveys include: The type, materials and dimensions of structural members (beams,

trusses or rafters)

Location and spacing between structural members

Thickness of roof surface and decking or membrane to structural members

Access to attic spaces to install blocking or additional structural support

Signs of structural issues include: Broken trusses or dips in the roof surface

Dry rot due to water leakage

Cracks in walls, columns or foundations


Fire Safety Codes

Fire safety codes impact the location of PV arrays on building rooftops, and address firefighter safety concerns.

Minimum setbacks are required for roof-mounted PV arrays and equipment to permit firefighters safe access, pathways and areas for smoke ventilation.

See: Solar Photovoltaic Installation Guideline, California Dept. of Forestry and

Fire Protection, Office of the State Fire Marshal: http://osfm.fire.ca.gov/pdf/reports/solarphotovoltaicguideline.pdf

Solar America Board for Codes and Standards: www.solarabcs.org


Fire Safety Codes:Residential Buildings

Access: Hip roofs shall have one (1), 3-foot wide clear access path from the eave

to the ridge on each roof slope where modules are located.

Single ridge roofs shall have two (2), 3-foot wide access paths from the eave to the ridge on each roof slope where modules are located.

Modules installed on both sides of hips or valleys shall be located no closer than 1½ feet to the hip or valley. Modules can be directly adjacent to a hip or valley if modules are located on only one side.

Ventilation: PV modules shall be located no higher than 3 feet below the ridge.

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Fire Safety Codes:Residential Gable Roof

Residential Gable Roof

CAL FIRE-OSFM

3’

3’

3’

3’


Fire Safety Codes:Residential Hip Roof

Residential Hip Roof

CAL FIRE-OSFM

3’

3’


Fire Safety Codes:Residential Cross Gable w/ Valley

Residential Cross Gable with Valley

CAL FIRE-OSFM

3’

3’

3’

3’

3’

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Fire Safety Codes:Residential Cross Gable Roof

Residential Cross Gable Roof

CAL FIRE-OSFM

3’

3’


Fire Safety Codes:Commercial Buildings

Access

A 6-foot wide clear perimeter shall be provided around the entire array, or a 4-foot clear perimeter is allowed where the shortest roof dimension is 250 feet or less.

Perimeter access is also usually provided for worker safety, shading and wind load concerns.



Pathways

Straight line clear pathways a minimum 4 feet wide and located over structural members shall be provided along the center line of both roof axes, and to skylights, ventilation hatches and standpipes.

A minimum of 4 feet clear space is also required around roof access hatches with at least one pathway not less than 4 feet clear pathway to parapet or roof edge.

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Ventilation

Arrays shall be no greater than 150 by 150 feet along either axis.

Ventilation options between array sections shall be either:

• A pathway eight feet or greater in width

• Four feet or greater in width pathway and bordering on existing roof skylights or ventilation hatches

• Four feet or greater in width pathway and bordering 4’ x 8’ “venting cutouts” every 20 feet on alternating sides of the pathway



Location of DC Conductors

To reduce trip hazards and maximize ventilation opportunities:

• Raceways and wiring systems should be located as close as possible to the ridge, hip or valley.

• Conduit runs between sub arrays and to DC combiner boxes should be as short as possible and minimized in pathways between the array.

DC wiring should be run in metallic conduit or raceways when located within a building to provide additional protection for venting operations.


Fire Safety Codes:Large Commercial Example

Large Commercial (Axis > 250’) 8’ Walkways

CAL FIRE-OSFM

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Fire Safety Codes:Large Commercial Example

Large Commercial (Axis > 250’) 4’ Walkways

With 8’ x 4’ Venting Opportunities Every 20’

CAL FIRE-OSFM


Fire Safety Codes:Small Commercial Example

Small Commercial (Axis < 250’) 8’ Walkways

CAL FIRE-OSFM


Fire Safety Codes:Small Commercial Example

Small Commercial (Axis < 250’) – 4’ Walkways

Venting Opportunities Every 20’ Along Walkway

CAL FIRE-OSFM

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Array Orientation

Maximum annual solar energy is received on a fixed surface that faces due south, and is tilted from the horizontal at an angle slightly less than the local latitude.

Autumn and winter performance is enhanced by tilting arrays at 15°greater than latitude.

Spring and summer performance is enhanced by tilting arrays 15° lower than latitude.

Fixed surfaces with azimuth orientations of ±45° degrees from due south and with tilt angles ±15° of local latitude will generally receive 90 to 95% or more of the annual solar energy as for optimally tilted south-facing surfaces.


Array Orientation

West

North

East

South

Zenith

South-facing array

Southwest-facing array

Tilt Angle

Azimuth Angle

Surface Normal

Surface Direction


Array Tilt Angle

West

North

East

South

Winter Solstice

Equinoxes

Summer Solstice

ZenithLatitude+15° tilt maximizes fall and winter performance

Close to Latitude tilt maximizes annual performance

Latitude-15° tilt maximizes spring and summer performance

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Array Tilt and Azimuth Angles

270 240 210 180 150 120 900

15

30

45

60

Azimuth (deg)

Tilt

(d

eg)

Available Irradiation (% of maximum)

95-100

90-95

85-90

80-85

75-80

70-75

270 240 210 180 150 120 900

15

30

45

60

Azimuth (deg)

Tilt

(d

eg)

Available Irradiation (% of maximum)

95-100

90-95

85-90

80-85

75-80

70-75

Miami, FL Boston, MA


Magnetic Declination

Magnetic declination is the angle between true geographic north and the magnetic north poles.

Magnetic declination varies with location and over time:

The western U.S. has positive, or easterly declination.

The eastern U.S. has negative, or westerly declination.

Magnetic declination is zero along a line running from Pensacola, FL to Duluth, MN, called an agonic line.


U.S. Magnetic Declination

USGS

East Declination

(positive)

West Declination

(negative)

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Magnetic Compass

Magnetic compass readings must be corrected for local magnetic declination.

The western U.S. has positive (eastern) declination, and will cause a compass needle to point east of the geographic north pole. West East

Geographic North

South - 180°

Magnetic North

270° 90°

0°

180°

Magnetic Declination (Positive, Eastern)


Shading Obstructions

Shading of PV arrays blocks usable solar energy and reduces array output.

Potential shading obstructions include: Trees and vegetation

Buildings and structures

Power lines, poles and towers

Roof-mounted obstructions including chimneys, vents, antennas and dormers

Other parts of the array

Sharp Solar


Shading Obstructions

Obstructions to the north can shade PV arrays during summer months early in the morning and late afternoon when the sun is in the northern part of the sky.

Shadows

FSEC

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Row Shading

A minimum separation distance is required to prevent multiple rack-mounted rows of PV arrays from shading one another.

Greater separation distances are required for taller arrays, higher latitudes, and to avoid shading for longer periods of the day.

FSEC/Jim Dunlop

Shadows


Row Shading

Spacing between rows (D) must be wide enough to prevent shading at low sun altitude from mid-morning until mid-afternoon around winter solstice.

D

Sun

PV Array H

North

South


Separation Distance

D

Separation Factor vs. Latitude for South-Facing Array Rows To Avoid Shading on Winter Solstice at Specified Solar Time

0

2

4

6

8

10

12

10 15 20 25 30 35 40 45 50 55 60

Latitude (deg N)

Sep

arat

ion

Fac

tor,

Dis

tan

ce/H

eig

ht

(D/H

) 8 am - 4 pm

9 am - 3 pm

10 am - 2 pm

11 am - 1 pm

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Solar Shading Analysis

Shading of PV modules and arrays reduces power and energy output.

PV arrays should be installed on surfaces that are unshaded between 9 a.m. and 3 p.m. solar time throughout the year.

Several tools are available to determine the extent of shading in the solar window:

Solar PathFinder: www.solarpathfinder.com

Solmetric SunEye: www.solmetric.com

Acme Solar Site Evaluation Tool (ASSET): www.we-llc.com


Solar Shading Calculators

Solar shading calculations are devices used to determine the extent of shading in the solar window.

Solar Pathfinder

Solmetric SunEye


Solar Shading Calculators

Wiley Electronics ASSETSolmetric SunEye 210

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Solar Pathfinder

Adjusting for Magnetic Declination

Leveling Base, Sunpath Chart and Glass Dome


Solar Pathfinder Diagram:Minimal Shading


Solar Pathfinder Diagram:Extensive Shading

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Solar Pathfinder AssistantSoftware

Site ReeportShading Measurement Locations


Solar Pathfinder AssistantSoftware

South View of Site

Obstruction Data for Individual Measurement


Solmetric SunEye 210

Digital shading analysis tool

Includes digital camera with fish eye lens, electronic compass, inclinometer and optional GPS.

Produces immediate results in the field, USB interface to PC software.

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Solmetric SunEye

Skyline Results

Solar Access Averages


Solmetric PV Designer Software


Site Layout

A site layout diagrams the property or facility for a planned PV system installation and identifies locations for the PV array and other equipment.

PV array location

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Energy Audit

Energy consumption for electrical loads are key factors in sizing stand-alone PV systems, and for grid-connected PV systems with battery storage for critical load backup.

Electrical Load Power (W) Avg. Daily Time of Use (hr) Avg. Daily Energy (watt-

hours) Lighting 200 6 1200 Refrigerator 300 9.6 (40% duty cycle) 2880 Microwave 1200 0.5 600 Pumps 1000 1 1000 TV and entertainment equipment

400 4 1600

Fans 300 6 1800 Washer 400 0.86 (3 hours 2 times per

week) 344

Miscellaneous plug loads 200 12 2400 Total all loads 4000 W (4 kW) 11,824 Wh (11.8 kWh)


Energy Use

Electric utility bills may be used to evaluate long-term energy consumption.

Watt and watt-hour meters may be used to measure the power demand and energy consumption for specific circuits and appliances.


Satellite Imagery for Site Surveys

Google Earth/Maps: www.google.com

Roof Ray: www.roofray.com

Local property appraiser’s websites

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Satellite Imagery

Satellite imagery can be used for PV system site surveys to find suitable areas for installing PV arrays, and to determine coordinates, distances and areas of buildings and properties.


Big Box Retail500 kW PV System

Home Depot: Daytona Beach, FL

270 ft

370 ft

Total roof area: 100,000 sq. ft.

If 50% of roof (50,000 sq. ft.) can be covered with PV, a 500 kW array can be installed.

A 500 kW PV array will produce enough energy on an average basis to meet the electrical load in typical light commercial retail.


Estimating Tools

PVWATTS:

http://rredc.nrel.gov/solar/codes_algs/PVWATTS/

In My Back Yard (IMBY):

www.nrel.gov/eis/imby/

Simple calculation:

DC Rating x DF = Peak AC Power Output (kW)

• Derating factor (DF) factor includes inverter efficiency losses and other derating factors, usually 0.75 to 0.85

Peak AC Power Output (W) x Peak Sun Hours = Energy Production (kWh/day)

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Estimating PV SystemEnergy Production

INTERACTIVE PV SYSTEM PERFORMANCE WORKSHEET

Estimating and Verifying System AC Energy Production

PV Array DC Power Rating at STC - 1000 W/m2, 25 °C (kW) 10

Derating FactorsNameplate Ratings 0.95Inverter and Transformer 0.95Module Mismatch 0.98DC Wiring 0.98AC Wiring 0.99Soiling 1.00Shading 0.85Sun Tracking 1.00Age 1.00

Combined Derating Factors 0.73

Estimated System AC Power Output at STC - 1000 W/m2, 25 °C (kW) 7.3

Temperature AdjustmentsArray Power-Temperature Coefficient (%/°C) -0.5Average Array Operating Temperature (°C) 45

Estimated System AC Power Output at 1000 W/m2 and Average Operating Temperature (kW) 6.6

Solar Radiation ReceivedSolar Irradiation in Plane of Array (kWh/m2/day) 5

Estimated System AC Energy Output at Average Operating Temperature (kWh/day) 29.5


PVWATTS Output

NREL


In My Backyard (IMBY)

NREL

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Software

Public Domain (NREL/DOE) PVWATTS: www.nrel.gov/rredc/pvwatts/

In My Back Yard (IMBY): www.nrel.gov/eis/imby/

HOMER: www.analysis.nrel.gov/homer/

Solar Advisor Model (SAM): www.nrel.gov/analysis/sam/

Commercial Clean Power Estimator: www.cleanpower.com

PVSYST: www.pvsyst.com

OnGrid: www.ongrid.net

PVSol: www.solardesign.co.uk/

PV F-Chart: www.fchart.com

Maui Solar Software: www.mauisolarsoftware.com/

Manufacturers Inverter string sizing and various system sizing and design tools


Installation Planning

Planning the installation process utilizes information gathered during a site survey, and includes:

Completing and adapting the system design.

Submitting applications for permits, utility interconnection and incentives.

Defining the project schedule, manpower and equipment needs.

Identifying and resolving construction activity conflicts such as power outages or alterations to the site.

Coordinating other logistics with the customer such as site access, worker facilities, waste collection and storage areas.


Summary

Site surveys involve an assessment of all issues relative to planning a PV installation.

Locations for PV arrays and other equipment are selected based on space, performance and code requirements.

A shading analysis evaluates the impacts of shading at potential PV array locations and helps estimate the reduced solar energy received.

The type and condition of a roofing system and structural support define the mounting system required.

Electrical services establish the allowable methods and maximum size of PV systems that can be interconnected at a site.

A site layout details the dimensions of site and locations for PV equipment.

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Questions and Discussion

Documents

Site Surveys and Preplanning - ECG...2018/04/03 · 7/27/2012 2 2012 Jim Dunlop Solar Site Surveys and Preplanning: 3 - 4 Site Surveys The objectives of a site survey include: Determine